1. The Field of the Invention
The invention relates to methods, apparatus, and systems for archiving data. Specifically, the invention relates to methods, apparatus, and systems for conducting incremental backups of data within a storage subsystem, independent of a host or file system.
2. The Relevant Art
Data processing systems are often required to copy large amounts of data to secondary storage or to another primary data store. Historically, copying entire volumes of data required that a system suspend all tasks that might access a source and/or a target volume. Suspension of the various tasks or processes to conduct the copy operation greatly reduced the performance of such systems.
Incremental backup techniques have been developed to lessen stoppage time and to increase system performance when archiving data. Incremental backup methods are typically conducted by software residing on the host, which monitors or detects storage volume changes at a file level. For example, an incremental backup process running on the host system may be required to scan all of the files within the file system in order to ascertain which blocks of data on the storage subsystem have changed since the last backup. To perform an incremental backup, any files that have been modified since the last backup are copied to a backup device such as a tape drive during a snapshot session.
Another method to reduce stoppage time while copying data from one volume to another is referred to as an instant copy, or “flashcopy.” An instant copy or flashcopy replicates data in a manner that appears instantaneous and allows a host to continue accessing a volume while actual data transfers are deferred to a later time. Flashcopy techniques typically defer the transfer of a data block to the secondary volume until a write operation is requested to that particular block on the primary volume. Until the actual data transfer occurs, read operations to the secondary volume are redirected to the primary volume. Flashcopy techniques greatly increase the performance of data processing systems and are conducted by the storage subsystem in a manner that is transparent to the host or file system.
In addition to increased performance, flashcopy capable systems simplify the code complexity of I/O intensive processes such as those conducted on large mainframe systems and the like. While extremely useful, conducting flashcopy operations directly to a backup device is not desirable in that the actual data is not immediately transferred to the backup device, thus leaving the system more vulnerable to various failures.
Despite the progress in backup systems, a need exists for a method of performing an incremental backup without requiring knowledge of files and access to the file system. Such a method would relieve the burden on the host computer of tracking and bookkeeping tasks and would facilitate efficient use of the backup resources while enabling access to the data involved in backup operations. In particular, what is needed is a method to leverage the capabilities of flashcopy techniques when performing incremental backups of data residing on storage subsystems.